Materialism is closely related to physicalism; the view that all that exists is ultimately physical. Philosophical physicalism has evolved from materialism with the discoveries of the physical sciences to incorporate far more sophisticated notions of physicality than mere ordinary matter, such as: spacetime, physical energies and forces, dark matter, and so on. Thus the term "physicalism" is preferred over "materialism" by some, while others use the terms as if they are synonymous.

Despite the large number of philosophical schools and subtle nuances between many,[1][2][3] all philosophies are said to fall into one of two primary categories, which are defined in contrast to each other: Idealism, and materialism.[a] The basic proposition of these two categories pertains to the nature of reality, and the primary distinction between them is the way they answer two fundamental questions: "what does reality consist of" and "how does it originate?" To idealists, spirit or mind or the objects of mind (ideas) are primary, and matter secondary. To materialists, matter is primary, and mind or spirit or ideas are secondary, the product of matter acting upon matter.[3]

The materialist view is perhaps best understood in its opposition to the doctrines of immaterial substance applied to the mind historically, famously by René Descartes. However, by itself materialism says nothing about how material substance should be characterized. In practice, it is frequently assimilated to one variety of physicalism or another.

Materialism is often associated with reductionism, according to which the objects or phenomena individuated at one level of description, if they are genuine, must be explicable in terms of the objects or phenomena at some other level of description — typically, at a more reduced level. Non-reductive materialism explicitly rejects this notion, however, taking the material constitution of all particulars to be consistent with the existence of real objects, properties, or phenomena not explicable in the terms canonically used for the basic material constituents. Jerry Fodor influentially argues this view, according to which empirical laws and explanations in "special sciences" like psychology or geology are invisible from the perspective of basic physics. A lot of vigorous literature has grown up around the relation between these views.

Modern philosophical materialists extend the definition of other scientifically observable entities such as energy, forces, and the curvature of space. However philosophers such as Mary Midgley suggest that the concept of "matter" is elusive and poorly defined.[4]

Materialism developed, possibly independently, in several geographically separated regions of Eurasia during what Karl Jaspers termed the Axial Age (approximately 800 to 200 BC).

In Ancient Indianphilosophy, materialism developed around 600 BC with the works of Ajita Kesakambali, Payasi, Kanada, and the proponents of the Cārvāka school of philosophy. Kanada became one of the early proponents of atomism. The Nyaya–Vaisesika school (600 BC - 100 BC) developed one of the earliest forms of atomism, though their proofs of God and their positing that the consciousness was not material precludes labelling them as materialists. Buddhist atomism and the Jaina school continued the atomic tradition.

Ancient Greek philosophers like Thales, Anaxagoras (ca. 500 BC – 428 BC), Epicurus and Democritus prefigure later materialists. The Latin poem De Rerum Natura by Lucretius (ca. 99 BC – ca. 55 BC) reflects the mechanistic philosophy of Democritus and Epicurus. According to this view, all that exists is matter and void, and all phenomena result from different motions and conglomerations of base material particles called "atoms" (literally: "indivisibles"). De Rerum Natura provides mechanistic explanations for phenomena such as erosion, evaporation, wind, and sound. Famous principles like "nothing can touch body but body" first appeared in the works of Lucretius. Democritus and Epicurus however did not hold to a monist ontology since they held to the ontological separation of matter and space i.e. space being "another kind" of being, indicating that the definition of "materialism" is wider than given scope for in this article.

Chinese thinkers of the early common era said to be materialists include Yang Xiong (53 BC – AD 18) and Wang Chong (c AD 27 – AD 100).

Later Indian materialist Jayaraashi Bhatta (6th century) in his work Tattvopaplavasimha ("The upsetting of all principles") refuted the Nyaya Sutra epistemology. The materialistic Cārvāka philosophy appears to have died out some time after 1400. When Madhavacharya compiled Sarva-darśana-samgraha (a digest of all philosophies) in the 14th century, he had no Cārvāka/Lokāyata text to quote from, or even refer to.[5]

Arthur Schopenhauer (1788-1860) wrote that "...materialism is the philosophy of the subject who forgets to take account of himself".[7] He claimed that an observing subject can only know material objects through the mediation of the brain and its particular organization. That is, the brain itself is the "determiner" of how material objects will be experienced or perceived:

"Everything objective, extended, active, and hence everything material, is regarded by materialism as so solid a basis for its explanations that a reduction to this (especially if it should ultimately result in thrust and counter-thrust) can leave nothing to be desired. But all this is something that is given only very indirectly and conditionally, and is therefore only relatively present, for it has passed through the machinery and fabrication of the brain, and hence has entered the forms of time, space, and causality, by virtue of which it is first of all presented as extended in space and operating in time."[8]

The German materialist and atheist anthropologist Ludwig Feuerbach would signal a new turn in materialism through his book, The Essence of Christianity (1841), which provided a humanist account of religion as the outward projection of man's inward nature. Feuerbach's materialism would later heavily influence Karl Marx.

Scientific "Materialism" is often synonymous with, and has so far been described, as being a reductive materialism. In recent years, Paul and Patricia Churchland have advocated a radically contrasting position (at least, in regards to certain hypotheses); eliminativist materialism holds that some mental phenomena simply do not exist at all, and that talk of those mental phenomena reflects a totally spurious "folk psychology" and introspection illusion. That is, an eliminative materialist might suggest that a concept like "belief" simply has no basis in fact - the way folk science speaks of demon-caused illnesses. Reductive materialism being at one end of a continuum (our theories will reduce to facts) and eliminative materialism on the other (certain theories will need to be eliminated in light of new facts), Revisionary materialism is somewhere in the middle.[9]

Some scientific materialists have been criticized, for example by Noam Chomsky, for failing to provide clear definitions for what constitutes matter, leaving the term "materialism" without any definite meaning. Chomsky also states that since the concept of matter may be affected by new scientific discoveries, as has happened in the past, scientific materialists are being dogmatic in assuming the opposite.[10]

The nature and definition of matter - like other key concepts in science and philosophy - have occasioned much debate.[11] Is there a single kind of matter (hyle) which everything is made of, or multiple kinds? Is matter a continuous substance capable of expressing multiple forms (hylomorphism),[12] or a number of discrete, unchanging constituents (atomism)?[13] Does it have intrinsic properties (substance theory),[14][15] or is it lacking them (prima materia)?

One challenge to the traditional concept of matter as tangible "stuff" came with the rise of field physics in the 19th century. Relativity shows that matter and energy (including the spatially distributed energy of fields) are interchangeable. This enables the ontological view that energy is prima materia and matter is one of its forms. On the other hand, the Standard Model of Particle physics uses quantum field theory to describe all interactions. On this view it could be said that fields are prima materia and the energy is a property of the field.

According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the "matter" described by the Standard Model of Particle Physics, and the majority of the universe is composed of dark matter and dark energy - with little agreement amongst scientists about what these are made of.[16]

With the advent of quantum physics, some scientists believed the concept of matter had merely changed, while others believed the conventional position could no longer be maintained. For instance Werner Heisenberg said "The ontology of materialism rested upon the illusion that the kind of existence, the direct 'actuality' of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible... atoms are not things." Likewise, some philosophers[which?] feel that these dichotomies necessitate a switch from materialism to physicalism. Others use the terms "materialism" and "physicalism" interchangeably.[17]

The concept of matter has changed in response to new scientific discoveries. Thus materialism has no definite content independent of the particular theory of matter on which it is based. According to Noam Chomsky, any property can be considered material, if one defines matter such that it has that property.[10]

In the twentieth century, physicalism has emerged out of positivism. Physicalism restricts meaningful statements to physical bodies or processes that are verifiable or in principle verifiable. It is an empirical hypothesis that is subject to revision and, hence, lacks the dogmatic stance of classical materialism. Herbert Feigl defended physicalism in the United States and consistently held that mental states are brain states and that mental terms have the same referent as physical terms. The twentieth century has witnessed many materialist theories of the mental, and much debate surrounding them.[18]

Some modern day physicists and science writers—such as Paul Davies and John Gribbin—have argued that materialism has been disproven by certain scientific findings in physics, such as quantum mechanics and chaos theory. In 1991, Gribbin and Davies released their book The Matter Myth, the first chapter of which, "The Death of Materialism", contained the following passage:

Then came our Quantum theory, which totally transformed our image of matter. The old assumption that the microscopic world of atoms was simply a scaled-down version of the everyday world had to be abandoned. Newton's deterministic machine was replaced by a shadowy and paradoxical conjunction of waves and particles, governed by the laws of chance, rather than the rigid rules of causality. An extension of the quantum theory goes beyond even this; it paints a picture in which solid matter dissolves away, to be replaced by weird excitations and vibrations of invisible field energy.

Quantum physics undermines materialism because it reveals that matter has far less "substance" than we might believe. But another development goes even further by demolishing Newton's image of matter as inert lumps. This development is the theory of chaos, which has recently gained widespread attention.

— Paul Davies and John Gribbin, The Matter Myth, Chapter 1

Davies' and Gribbin's objections are shared by proponents of digital physics who view information rather than matter to be fundamental. Their objections were also shared by some founders of quantum theory, such as Max Planck, who wrote:

As a man who has devoted his whole life to the most clear headed science, to the study of matter, I can tell you as a result of my research about atoms this much: There is no matter as such. All matter originates and exists only by virtue of a force which brings the particle of an atom to vibration and holds this most minute solar system of the atom together. We must assume behind this force the existence of a conscious and intelligent Mind. This Mind is the matrix of all matter.

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According to the Catholic Encyclopedia, materialism denies the existence of both deities and "souls".[19] It is therefore incompatible with most world religions, including Christianity, Judaism, and Islam. In most of Hinduism and transcendentalism, all matter is believed to be an illusion called Maya, blinding us from knowing the truth. Maya is the limited, purely physical and mental reality in which our everyday consciousness has become entangled. Maya gets destroyed for a person when s/he perceives Brahman with transcendental knowledge. In contrast, Joseph Smith, the founder of the Latter Day Saint movement, taught "There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes; We cannot see it; but when our bodies are purified we shall see that it is all matter."[20] This spirit element has always existed; it is co-eternal with God.[21] It is also called intelligence or the light of truth, which like all observable matter "was not created or made, neither indeed can be."[22] Members of The Church of Jesus Christ of Latter-day Saints view the revelations of Joseph Smith as a restoration of original Christian doctrine, which they believe began to be corrupted at the hands of post-apostolic theologians in the centuries after Christ. The writings of many of these theologians indicate a clear influence of Greek metaphysical philosophies such as Neoplatonism, which characterized divinity as an utterly simple, immaterial, formless, substance/essence (ousia) that transcended all that was physical.[23] Despite strong opposition from many Christians,[24] this metaphysical depiction of God eventually became incorporated into the doctrine of the Christian church, displacing the original Judeo-Christian concept of a physical, corporeal God who created humans in His image and likeness.[25]

Kant argued against all three forms of materialism, subjective idealism (which he contrasts with his "transcendental idealism"[26]) and dualism.[27] However, Kant also argues that change and time require an enduring substrate,[28] and does so in connection with his Refutation of Idealism.[29]Postmodern/poststructuralist thinkers also express a skepticism about any all-encompassing metaphysical scheme. Philosopher Mary Midgley,[30] among others,[31][32][33][34] argues that materialism is a self-refuting idea, at least in its eliminative form.

An argument for idealism, such as those of Hegel and Berkeley, is ipso facto an argument against materialism. Matter can be argued to be redundant, as in bundle theory, and mind-independent properties can in turn be reduced to subjective percepts. Berkeley presents an example of the latter by pointing out that it is impossible to gather direct evidence of matter, as there is no direct experience of matter; all that is experienced is perception, whether internal or external. As such, the existence of matter can only be assumed from the apparent (perceived) stability of perceptions; it finds absolutely no evidence in direct experience.

If matter and energy are seen as necessary to explain the physical world, but incapable of explaining mind, dualism results. Emergence, holism, and process philosophy seek to ameliorate the perceived shortcomings of traditional (especially mechanistic) materialism without abandoning materialism entirely.

Some critics object to materialism as part of an overly skeptical, narrow or reductivist approach to theorizing, rather than to the ontological claim that matter is the only substance. Particle physicist and Anglican theologianJohn Polkinghorne objects to what he calls promissory materialism — claims that materialistic science will eventually succeed in explaining phenomena it has not so far been able to explain.[35] Polkinghorne prefers "dual-aspect monism" to faith in materialism.[36]

^see Critique of Pure Reason where he gives a "refutation of idealism" in pp345-52 (1st Ed) and pp 244-7 (2nd Ed) in the Norman Kemp Smith edition

^Critique of Pure Reason (A379, p352 NKS translation). "If, however, as commonly happens, we seek to extend the concept of dualism, and take it in the transcendental sense, neither it nor the two counter-alternatives — pneumatism [idealism] on the one hand, materialism on the other — would have any sort of basis [...] Neither the transcendental object which underlies outer appearances nor that which underlies inner intuition, is in itself either matter or a thinking being, but a ground (to us unknown)..."

^"Kant argues that we can determine that there has been a change in the objects of our perception, not merely a change in our perceptions themselves, only by conceiving of what we perceive as successive states of enduring substances (see Substance)".Routledge Encyclopedia of Philosophy

^"All determination of time presupposes something permanent in perception. This permanent cannot, however, be something in me [...]" Critique of Pure Reason, B274, P245 (NKS translation)